Chlorpropham is a herbicide used on several crops to control annual grasses and manybroad-leaved weeds. The release of chlorpropham in the environment occurs during itsmanufacture and particularly from its use in the field. Chlorpropham adsorbs strongly to soil andclays and will exhibit low mobility in soil. In soil, chlorpropham is transformed primarily bybiodegradation. The half-life of chlorpropham from field soil is about 30 days. If released in water,chlorpropham will adsorb strongly to sediment and particulate matter in the water column.Although a slow process, biodegradation should be the major pathway for degradation. Loss ofchlorpropham due to hydrolysis, photolysis and volatilization should not be important lossprocesses. Chlorpropham will not bioconcentrate in aquatic organisms. In the atmosphere,chlorpropham will react with hydroxyl radicals with an estimated half-life of 5.5 hrs. Partialremoval of atmospheric chlorpropham will also occur by dry and wet deposition. Chlorprophamhas been infrequently detected in groundwater around sprayed farmlands. Workers who applychlorpropham are the most likely people to be exposed to chlorpropham. Exposure would beexpected by inhalation and dermal contact. The general population may be exposed to low levelsof chlorpropham in food.

Environmental Fate

TERRESTRIAL FATE: Biodegradation via enzymatic hydrolysis will be the majorprocess by which chlorpropham will be lost from most soils . The loss of chlorpropham fromsoil due to photolysis on soil surface may not be important . Vaporization loss of chlorprophamfrom dry soil should be negligible, but increases with increase in temperature, moisture contentand air flow rate . The leaching of chlorpropham from three types of soil was low and morethan 90% of chlorpropham was found in the upper inch of the soil after 4 cm of rain .Depending on the nature of soil and climatic conditions, the field half-life of chlorpropham in soilrange from less than 30 days to 65 days with an average half-life of 30 days . AQUATIC FATE: Based on a mean rate constant of 2.6X10-14 l/organism-hr and a bacterialconcn of 5X10 8 organisms/l in water, the half-life of chlorpropham has been estimated to be2208 days . Therefore, biodegradation of chlorpropham should not be important in clear bodiesof water. However, biodegradation may become important if the bacterial population inwater is several orders of magnitude higher than 10 8 organisms . The hydrolysis half-life ofchlorpropham in the pH range 5-9 has been estimated to be greater than 10000 days . Theestimated minimum half-life for the direct sunlight photolysis of chlorpropham in clear surfacelayers of water is 121 days . Based on the available data , it is concluded that biodegradationmay be the dominant degradation pathway for chlorpropham in polluted waters, but photolysismay become the dominant degradative pathway in unpolluted waters. Based upon themoderate water solubility (89 ppm) and the low vapor pressure (7.5X10-6 mmHg) ,chlorpropam should not volatilize from water or bioconcentrate in aquatic organisms(5,SRC). ATMOSPHERIC FATE: From its estimated vapor pressure of 7.5X10-6 mm Hg at 25 degC(1,4), chlorpropham is expected to be present partially in the vapor phase and partially in theparticulate form in air(2,SRC). Based on an estimation method(3,5), vapor phase chlorprophamshould be removed from the atmosphere with an estimated half-life of 5.5 hrs due to reaction withphotochemically produced hydroxyl radicals. Partial removal of particulate chlorprophamfrom the air may occur by dry deposition. Chlorpropham may also be washed out of the airby rain. MOIST SOIL TREATED WITH CHLOROPROPHAM TO GIVE CONCN OF 100 PPM AIWAS INCUBATED IN POLYETHYLENE BAGS @ 23 DEG C FOR 30 WK. CO2EVOLUTION WAS DETERMINED WEEKLY. CHLOROPHAM WAS DEGRADEDRAPIDLY IN FIRST 6WK & 5% OF ORIGINAL AMT COULD BE DETECTED 30 WKLATER.

Drinking Water Impact

GROUNDWATER: Chlorpropham has been detected in one groundwater sample from28 of California's 58 counties at a concn of 8.0 ug/l(1-3).